Fabricating semiconductors chips is a multi-step process. Silicon wafers, sliced from a crystal ingot, initially are lapped flat and polished to a mirror-like finish. A layer of single crystalline silicon subsequently is grown on each wafer and the wafers oxidized at elevated temperatures approaching 1000.degree. C. A light-sensitive, "photo-resist" coating then may be applied to each wafer and a wafer stepper used to expose the photo-resist coating. Exposing the coating produces multiple prints containing images of several integrated chips on each wafer.
Following exposure, the photo-resist coatings are developed and baked to harden the patterned prints onto the silicon wafers. The wafers then contact a reactive gas discharge, etching exposed portions of the wafers, before having ionized boron atoms or other impurities implanted into the patterns. A low temperature (350.degree. C.) plasma discharge deposits silicon dioxide on the wafers at low pressure, while circuit component contacts may be made by depositing onto the wafers a thin aluminum or similar metallic film. Each wafer later may be cut into multiple semiconductor chips using a precision diamond saw and the chips attached to packages having contact leads and wire connections. Finally, each chip is then encapsulated in plastic for mechanical and environmental protection.
Because even microscopic airborne impurities can degrade the quality and yield of the fabricated chips, many of these manufacturing steps, including those of applying the photoresist coating to the wafers and exposing integrated chip images on the coatings, are performed in facilities called "clean rooms." The atmospheres of these clean rooms generally are regulated to limit the numbers and types of particles capable of contacting the silicon wafers. Bodies of workers operating in clean rooms, for example, typically are enveloped by sterile clothing to prevent skin, hair, and other personal particulate matter from being deposited on the wafers. Additional Humidity/Ventilation/Air Conditioning (HVAC) equipment may be used to condition air within the clean rooms to reduce particle concentrations resulting from other sources of contamination such as the wafer processing and handling machinery.
An average manufacturing facility may include as many as two hundred pieces of processing and handling equipment for fabricating semiconductor chips. To accommodate both the various equipment used to process the wafers and wafer-handling personnel, the size of many clean rooms frequently may approach 20,000 ft.sup.2. Such rooms are costly to construct, requiring sophisticated monitoring and air conditioning equipment to regulate, even moderately, the large-scale environments. Moreover, although clean rooms may be erected to meet present governmental and industry standards mandating less than or equal to 7.5 particles of 0.2 microns or larger per cubic foot, many do not, and cannot, be constructed to fulfill the more rigorous decontamination standards required to produce, for example, 64-megabit dynamic random-access memory chips (DRAMs). Existing clean room technology similarly cannot protect work pieces and material-handling personnel from many microscopic contaminates, including bacteria and viruses, present in the medical, pharmaceutical, biotechnological, food preparation, aerospace, and other processing industries.